1. Field of the Invention
The present invention relates to a power-supply circuit and a test apparatus. More specifically, the invention relates to a power-supply circuit for supplying voltage to a load and a test apparatus for testing a device-under-test.
2. Related Art
Conventionally, there has been known a power-supply circuit for supplying predetermined voltage to a load by using a switching amplifying circuit (Takamasa Hori, Inter-University Power Electronics, First Edition, Ohmsha Ltd., December, 1996, pp. 85-102). Such power-supply circuit supplies the predetermined voltage to the load by switching, by means of a switch, a case of supplying the predetermined voltage to the load as power-supply voltage generated by a power supply accumulates electromagnetic energy in an inductance provided on a circuit and a case of supplying the predetermined voltage to the load by disconnecting the power supply from the load and by regenerating the current by using the electromagnetic energy accumulated in the inductance. Then, in such power-supply circuit, the voltage V0 supplied to the load may be represented by means of a duty ratio D between a first switch for connecting the power-supply voltage to the inductance and a second switch for regenerating the current by the inductance, and of the power-supply voltage Vs as V0=Vs×D.
Although the conventional power-supply circuit is capable of controlling the voltage V0 to be supplied to the load by controlling the duty ratio D, it has been unable to freely select positive voltage and negative voltage and to supply them to the load by using single power supply because a polarity of the V0 is decided by a polarity of the power-supply voltage Vs.
The voltage supplied to the load also varies due to connection and disconnection of the switches in the power-supply circuit using the switching amplifying circuit. Accordingly, output ripple voltage in the voltage supplied to the load is not zero and noise components of the power-supply circuit caused by the output ripple voltage have been a problem.